New studies indicate that lead is detrimental to child development at lower levels than previously believed. Lead crosses the placenta freely, and the fetus may be threatened by maternal blood lead even at low levels. Prenatal exposure may be critical because fetal development, especially of the central nervous system, is rapid and sensitive to many toxicants; the effects of prenatal exposure may continue into the postnatal period. At present little is known about the dynamics of maternal blood lead levels during the course of pregnancy, the child's lead burden at birth, and the child's subsequent development. The objectives of this epidemiologic study are to identify the maternal characteristics which determine fetal exposure to lead and to identify the effects of pre- and postnatal lead exposure on early human development. Specifically, we will determine: 1) the pattern of changes in mother's blood lead levels during pregnancy, and the influences on these changes of maternal nutritional, anthropometric and socioeconomic characteristics; 2) the relationship of the child's neonatal and postnatal lead levels to maternal serum lead levels, maternal nutritional, anthropometric, and socioeconomic characteristics, and race; 3) the relationship of mother's and child's lead levels to the child's cognitive/behavioral development and to their physical growth, and 4) whether any cognitive/behavioral deficits are mediated through lead- associated delays in physical growth. The study employs a longitudinal design, following mothers from mid-pregnancy through delivery and their children from birth through one year of age. Blood lead levels of the mother and child and the child's physical growth and cognitive/behavioral development will be measured serially throughout the study period. Multivariate statistical techniques and structural equation analysis will be used to determine the relationship among lead levels at different times, maternal characteristics, and child development measures.